Mobile mining equipment such as mining excavators and off road haul trucks is used during mining operations. Mining excavators such as electric shovels and draglines draw a significant amount of electrical power during mining operations. The power drawn by a mining excavator presents a cyclic load to an electrical power distribution network. The cyclic load may include at least one motoring interval (wherein power is drawn from a power source) and one regenerating interval (wherein power is returned to the power source) Electrical power generated by the mining excavator during the regeneration interval is captured and used to charge an on-board electrical energy storage system.
Mining haul trucks are typically equipped with an electrical drive system that includes electric motors which drive the truck wheels. The haul truck draws electrical power from an electrical generator powered by the truck engine or an overhead trolley line while propelling. During downhill travel, the electric motor brakes and this braking power is captured and used to charge an on-board electrical energy storage system.
The system or device used for energy storage is an important area of concern in mobile mining applications. As an example, mining excavators or haul trucks frequently operate in remote locations with extreme climatic conditions where temperatures may go as low as 20° C. below zero. This puts a severe strain on traditional energy storage systems that utilize batteries and associated systems which are used for backup power for various electronic systems and components in the mining excavator such as computers, displays, control systems, protection systems and others.
As an example, the control power and backup power for gas insulated switchgear (GIS) used in a mining excavator is typically provided by lead-acid DC batteries. Such batteries are sufficient for normal conditions but have substantial disadvantages when used in severe cold weather conditions since the acid in the batteries is susceptible to freezing. In order to avoid this, the batteries are typically stored in a heated compartment. However, if a prolonged power outage occurs the temperature of the compartment is no longer controlled which leads to freezing and ultimately battery failure.
As previously described, the regenerated power produced by an excavator or a haul truck may be stored as energy in an energy storage system. This stored energy could be used to reduce the peak power demanded by the electric motors in an excavator or haul truck. Referring to FIG. 11, a typical duty cycle for an electric shovel is shown as power plot 1200. As can be seen, the power profile for the electric shovel indicates a cycle time of approximately 32 seconds. This indicates that the energy storage system should have the capability to charge and discharge every 32 seconds. However, subjecting a conventional battery to such frequent charge/discharge cycles undesirably reduces battery life. Another disadvantage of using batteries is that they require regular maintenance. In addition to reducing peak power demand, the stored energy could be used as an auxiliary power source for various system critical components like protection system, control system etc.
Alternatively, capacitors have been considered for use in an energy storage system instead of batteries. However, the power requirements of a mining excavator would require the use of very large capacitors. This is undesirable since shovels are mobile machines and size and weight are important parameters in shovel design.